Accumulation of β-1,3-glucanase and chitinase isoforms, and salicylic acid in the DL-β-amino-n-butyric acid-induced resistance response of pepper stems to Phytophthora capsici

Pepper (Capsicum annuum L.) plants sprayed with DL-beta-amino-n-butyric acid (BABA) were protected against Phytophthora capsici infection. BABA treatment induced the synthesis and accumulation of beta-1,3-glucanases and chitinases in the stem tissues of pepper plants. Their accumulation was very pronounced in the stems challenge-inoculated with P. capsici after BABA treatment. Several beta-1,3-glucanase and chitinase isoforms accumulated in BABA treated P. capsici. When analysed by immunoblot of the denatured proteins, the 20 kDa beta-1,3-glucanase and 32 kDa chitinase were found in pepper stems treated with BABA and/or infected by P. capsici. BABA treatment did not stimulate capsidiol production in pepper stems, but prior treatment led to high accumulation in P. capsici-infected ones. Unlike capsidiol production, BABA treatment triggered a dramatic increase in the endogenous levels of salicylic acid (SA) in pepper stems. The increase in endogenous SA was much pronounced in P. capsici infected stems after BABA treatment. In conclusion, the induction of resistance to P. capsici in pepper plants by BABA treatment positively correlated with the accumulation of certain beta-1,3-glucanase and chitinase isoforms, and SA. These results suggest strongly that SA may act as an endogenous signal responsible for activating particular components of resistance to P. capsici and the induction of pathogenesis-related proteins such as beta-1,3-glucanase and chitinase. (C) 1997 Academic Press Limited.